In recent years treatment of aneurysms has included the use of stent grafts that are emplaced within the vascular networks and that include one or more stents affixed to graft material. The stent grafts are secured at a treatment site by endovascular insertion utilizing introducers and catheters, whereafter they are enlarged radially and remain in place by self-attachment to the vessel wall. In particular, stent grafts are known for use in treating descending thoracic and abdominal aortic aneurysms where the stent graft at one end defines a single lumen for placement within the aorta and at the other end is bifurcated to define two lumens, for extending into the branch arteries.
One example of such a stent graft is disclosed in PCT Publication No. WO 98/53761 in which the stent graft includes a sleeve or tube of biocompatible graft material such as Dacron™ polyester fabric (trademark of E. I. DuPont de Nemours and Co.) or polytetrafluoroethylene defining a lumen, and further includes several stents secured therealong, with the stent graft spanning the aneurysm extending along the aorta proximally from the two iliac arteries; the reference also discloses the manner of deploying the stent graft in the patient utilizing an introducer assembly. The graft material-covered portion of the single-lumen proximal end of the stent graft bears against the wall of the aorta above the aneurysm to seal the aneurysm at a location that is spaced distally of the entrances to the renal arteries. Thin wire struts of a proximal stent extension traverse the renal artery entrances without occluding them, since no graft material is utilized along the proximal stent while securing the stent graft in position within the aorta when the stent self-expands. An extension is affixed to one of the legs of the stent graft to extend along a respective iliac artery and, optionally, extensions may be affixed to both legs. Another known stent graft is the Zenith AAA™ stent graft sold by William A. Cook Australia Pty., Brisbane, Australia.
In prior art stent grafts, graft fixation was achieved by fixation at the top or proximal end by barbs or by a stent portion that is uncovered by graft material and could be incorporated into the vessel wall. Distal end fixation was attained by friction within the branch or iliac arteries. The stents of the prior art stent grafts tended to be flexible and relatively soft. The proximal main tube graft was of a standardized length, and that length tended to be significantly shorter than the aneurysms themselves, while the full length was bridged and achieved by smaller diameter extensions or legs.
With the prior art stent grafts, certain late complications were common: due to the above-mentioned configuration there was a certain instability leading to kinking, obstruction of the lumen and/or disintegration leading to possible graft explantation, wherein the stent graft undesirably moved out of its intended position mostly due to larger displacement forces within the smaller diameter stent graft portions; material fatigue also occurred, leading to endoleak wherein blood flow continued into the aneurysm.